The present invention relates to an ion source and a method of implanting ions therefrom into a semiconductor substrate. The present invention is particularly useful in extending the life of an ion source.
Conventional semiconductor devices comprise a substrate in which individual circuit components are formed and various interconnection patterning formed thereon. The formation of various circuit components and interconnection patterns is partly accomplished by employing conventional photolithography, etching and implantation techniques. The density of integrated circuits and their speed of operation are dependent largely upon the accuracy and resolution of the photolithography and etching apparatuses used to form patterns of circuit elements and masking layers on the semiconductor wafer. However, density and speed are also dependent upon achieving tight control of the profile of doped regions in the semiconductor substrate.
Ion implantation systems are conventionally employed to modify the electrical properties in a region of a semiconductor substrate by implanting an impurity dopant into the substrate which elicits the desired electrical modification. The type of dopant profiles, concentrations and lateral geometries required on a very large scale integration (VLSI) or ultra large scale integration (ULSI) make ion implantation the doping process most conducive to providing uniformity and repeatability thereby dramatically improving fabrication yields. Improved ion implantation systems has, therefore, become critical in the fabrication of higher integrated devices, e.g. devices having a design rule of about 0.25 xcexcand under.
FIG. 1 illustrates a conventional ion implantation system used for the manufacture of semiconductor devices. As shown in FIG. 1, the ion implantation system includes ion source 10, ion beam 12, beam-analyzing system 14, beam conditioning system 16 and implantation station 18. The process for implanting a particular ion into a semiconductor substrate begins by introducing a feed material to ion source 10 to generate an ionized gas (or plasma) of the feed material. The plasma generated by the ion source contains a mixture of ions from which the desired ion must be separated. Separation is typically achieved by extracting ions from the generated plasma, forming a beam of the extracted ions, shown as numeral 12, and accelerating the ion beam toward mass analyzing system 14, wherein the mixture of ions is separated based on mass to form a beam of particular ions for implantation. Beam conditioning system 16 resolves, focuses and accelerates the desired particular ions to implantation station 18 wherein a semiconductor substrate is targeted and the desired ions are implanted. A more complete description of ion implantation systems and their component parts can be found in U.S. Pat. Nos. 4,578,589 and 5,554,854.
A significant factor which determines throughput of semiconductor devices in an ion implanter is the generation of the ion beam itself. As discussed above, the ion beam is generated by an ion source which comprises an ionizing chamber having entrance and exit ports and a filament contained within the ionizing chamber for transferring electrons to a gaseous feed material introduced into the chamber thereby generating an ionized gas of the feed material. A more complete description of ion sources can be found in U.S. Pat. Nos. 5,252,892; 5,306,921 and 5,656,820 which are herein incorporated by reference.
Under normal operating conditions, however, the inner surfaces of an ion source are damaged from the generated plasma. In particular, ions, radicals and excited species of the plasma causes etching or sputtering of structural surfaces within the chamber. Vaporized metal material deposits on insulators and vaporized insulating materials deposit on electrically conductive element resulting in shorting, arcing and ultimate failure of the device. Moreover, the feed material itself generates undesirable polymeric deposits within the ion source further exacerbating device failure over a period of time. The problem is particularly acute in systems employing corrosive and/or highly fluorinated feed materials, such as BF3 and GeF4.
Conventional remedial procedures comprise routinely cleaning the ion source to remove or reduce damaging forming deposits on interior parts to prevent device failure. Removing contaminated materials from the ion source requires stopping the ion implantation system and replacing the contaminated ion source with a pre-cleaned source, which is commonly referred to as a xe2x80x9cchange-outxe2x80x9d. A change-out process, however, disrupts the manufacturing process in that the implantation operation must cease during the change-out procedure. In addition to stopping the implantation operation and replacing the contaminated ion source, precise alignment of the implantation system and conditioning of the interior atmosphere thereof must be achieved prior to resuming proper operation of the system. Typically, a complete change-out procedure can take up to eight hours. The change-out procedure represents a significant economic cost in terms of semiconductor through-put and down time. Further, the removed contaminated ion source must be disassembled, and the component parts cleaned and reassembled. The reconditioning of the ion source can take another additional eight hours further adding to the cost of operation.
Accordingly, a need exists for ion implantation methodologies in which damaging deposits generated during the operation of an ion source are reduced to prevent device failure. A need also exists for increasing the length of time that an ion source can be operated before requiring reconditioning.
An advantage of the present invention is an improved ion source. The improved ion source reduces damaging deposits and provides a longer operating beam time.
Additional advantages and other features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the invention. The advantages of the invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by an ion source comprising: an electrically conductive chamber for forming ions having at least two ports, wherein the first port allows the introduction of materials and the second port allows the escape of an ion; a filament in the electrically conductive chamber and insulated therefrom; a power source connected to the filament for generating an electrical discharge; and a source of oxygenated gas fluidly connected to the electrically conductive chamber for supplying an oxygenated gas to the chamber.
Another aspect of the present invention is a method of operating an ion source comprising a chamber and a filament contained therein. The method comprises supplying an oxygenated gas to the chamber. The method advantageously comprises operating the ion source for an extended beam time of no less than two times the normal operating beam time and up to a multiple of about five times or more the normal operating beam time.
A further aspect of the present invention is a method for reducing contaminant formation within an ion source comprising a chamber and a filament contained therein. The method comprises: reducing the pressure of the chamber to below atmospheric pressure; introducing a feed material to the chamber; introducing an oxygenated gas to the chamber; applying electrical power to the filament to form ions of the feed material; and reacting the oxygenated gas with contaminant forming deposits within the chamber. The method advantageously comprises reacting the oxygenated gas with polymer forming ions or radicals, or with metal forming deposits within the chamber thereby preventing damaging deposits from coating structural elements in the chamber and decreasing the life-time of the ion source.
Additional advantages of the present invention will become readily apparent to those having ordinary skill in the art from the following detailed description, wherein the embodiments of the present invention are described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments and its several details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.